Currently, there is a requirement that zoom lenses used for digital still cameras, surveillance TV cameras, cameras for portable terminals, video cameras, and similar imaging devices that use an imaging element, such as a CCD or a CMOS, be made smaller, lighter, and with reduced manufacturing costs. For example, Japanese Laid-Open Patent Applications H05-164965, H07-281093, and H09-184979 disclose two-group zoom lenses with two lens elements, Japanese Laid-Open Patent Applications H06-148518 and H11-23966 disclose two-group zoom lenses with three lens elements, and Japanese Laid-Open Patent Applications 2000-330019 and 2002-014285 disclose three-group zoom lenses with five lens elements that may be used to meet this requirement.
However, even though the above described zoom lenses with either a two-group, two lens element construction or a two-group, three lens element construction are able to meet the requirement of miniaturization and lighter weight, there is room for further improvement concerning the correction of various aberrations such as longitudinal chromatic aberration, curvature of field, and distortion.
Additionally, because the number of lens groups and lens elements used in such zoom lenses has become large, for example, three lens groups and five lens elements as disclosed in Japanese Laid-Open Patent Application 2002-014285, further development of a smaller and lighter weight zoom lens is desired.
Accordingly, a zoom lens with a three-group, three or four lens element construction and that is small, light in weight, and that satisfactorily corrects various aberration is required. Japanese Laid-Open Patent Application H05-323190 and Japanese Laid-Open Patent Application H06-289290 are directed to such requirements.
In a zoom lens used for a digital still camera or similar imaging device that uses a CCD or a CMOS image pickup element, the light exiting the image-side lens surface toward the image plane should be nearly parallel, that is, nearly at a zero exit angle, to the optical axis of the zoom lens. Thus, a smaller exit angle than that provided by conventional zoom lenses is desired. Additionally, a higher zoom ratio is desired, as well as a reduction in the conjugate distance to the image plane.